Place the cut chicken breasts into the bottom of a 6-quart slow cooker.

In a large bowl, whisk together the cream of chicken soup, heavy cream, milk, Italian dressing mix, garlic powder, and black pepper until smooth. Pour this mixture over the chicken in the slow cooker.

Add the chicken broth and sun-dried tomatoes to the slow cooker. Stir gently to combine all ingredients.

Cover and cook on LOW for 6 to 8 hours, or on HIGH for 3 to 4 hours, until the chicken is cooked through and easily shreddable.

Remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken to the sauce.

While the chicken cooks, cook the penne pasta according to package directions until al dente. Drain well.

Stir the drained pasta, 3/4 cup of the Parmesan cheese, and the optional spinach (if using) into the slow cooker mixture. Cook on the WARM setting for another 10-15 minutes until the spinach wilts and the Parmesan is melted.

Taste and adjust seasoning if necessary. Serve immediately, garnished with the remaining Parmesan cheese.